INTERIM: Macros instead of const for global COOP defaults.

Author: peter-lyons-kehl

library/alloc/src/boxed.rs

@@ -146,7 +146,6 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::alloc;
 use core::any::Any;
 use core::async_iter::AsyncIterator;
 use core::borrow;
@@ -776,9 +775,10 @@ where
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
     #[must_use]
+    #[allow(unused_braces)]
     pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
         unsafe {
-            RawVec::<T, A, { alloc::SHORT_TERM_VEC_PREFERS_COOP }>::with_capacity_in(len, alloc)
+            RawVec::<T, A, { SHORT_TERM_VEC_PREFERS_COOP!() }>::with_capacity_in(len, alloc)
                 .into_box(len)
         }
     }
@@ -807,9 +807,10 @@ where
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
     #[must_use]
+    #[allow(unused_braces)]
     pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
         unsafe {
-            RawVec::<T, A, { alloc::SHORT_TERM_VEC_PREFERS_COOP }>::with_capacity_zeroed_in(
+            RawVec::<T, A, { SHORT_TERM_VEC_PREFERS_COOP!() }>::with_capacity_zeroed_in(
                 len, alloc,
             )
             .into_box(len)

library/alloc/src/collections/binary_heap/mod.rs

@@ -148,13 +148,14 @@ use core::mem::{self, swap, ManuallyDrop};
 use core::num::NonZeroUsize;
 use core::ops::{Deref, DerefMut};
 use core::ptr;
-use core::{alloc, fmt};
+use core::fmt;
 
 use crate::alloc::Global;
 
 use crate::collections::TryReserveError;
 use crate::slice;
 use crate::vec::{self, AsVecIntoIter, Vec};
+use crate::DEFAULT_COOP_PREFERRED;
 
 use super::SpecExtend;
 
@@ -1243,7 +1244,8 @@ impl<T> BinaryHeap<T> {
     /// ```
     #[inline]
     #[stable(feature = "drain", since = "1.6.0")]
-    pub fn drain(&mut self) -> Drain<'_, T, { alloc::SHORT_TERM_VEC_PREFERS_COOP }> {
+    #[allow(unused_braces)]
+    pub fn drain(&mut self) -> Drain<'_, T, { SHORT_TERM_VEC_PREFERS_COOP!() }> {
         Drain { iter: self.data.drain(..) }
     }
 
@@ -1652,7 +1654,8 @@ impl<T: Ord, const N: usize> From<[T; N]> for BinaryHeap<T> {
 }
 
 #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
-impl<T> From<BinaryHeap<T>> for Vec<T, Global, DEFAULT_COOP_PREFERRED> {
+#[allow(unused_braces)]
+impl<T> From<BinaryHeap<T>> for Vec<T, Global, {DEFAULT_COOP_PREFERRED!()}> {
     /// Converts a `BinaryHeap<T>` into a `Vec<T>`.
     ///
     /// This conversion requires no data movement or allocation, and has

library/alloc/src/collections/vec_deque/drain.rs

@@ -15,11 +15,12 @@ use super::VecDeque;
 ///
 /// [`drain`]: VecDeque::drain
 #[stable(feature = "drain", since = "1.6.0")]
+#[allow(unused_braces)]
 pub struct Drain<
     'a,
     T: 'a,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
-    const COOP_PREFERRED: bool = { alloc::SHORT_TERM_VEC_PREFERS_COOP },
+    const COOP_PREFERRED: bool = { SHORT_TERM_VEC_PREFERS_COOP!() },
 > where
     [(); alloc::co_alloc_metadata_num_slots_with_preference_specific::<A>(COOP_PREFERRED)]:,
 {

library/alloc/src/collections/vec_deque/mod.rs

@@ -7,7 +7,7 @@
 
 #![feature(global_co_alloc)]
 #![stable(feature = "rust1", since = "1.0.0")]
-use crate::vec::DEFAULT_COOP_PREFERRED;
+use crate::DEFAULT_COOP_PREFERRED;
 use core::alloc;
 use core::cmp::{self, Ordering};
 use core::fmt;
@@ -93,10 +93,11 @@ mod tests;
 #[cfg_attr(not(test), rustc_diagnostic_item = "VecDeque")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_insignificant_dtor]
+#[allow(unused_braces)]
 pub struct VecDeque<
     T,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
-    const COOP_PREFERRED: bool = DEFAULT_COOP_PREFERRED,
+    const COOP_PREFERRED: bool = {DEFAULT_COOP_PREFERRED!()},
 > where
     [(); alloc::co_alloc_metadata_num_slots_with_preference_specific::<A>(COOP_PREFERRED)]:,
 {

library/alloc/src/ffi/c_str.rs

@@ -17,6 +17,8 @@ use core::ptr;
 use core::slice;
 use core::slice::memchr;
 use core::str::{self, Utf8Error};
+use crate::Global;
+use crate::DEFAULT_COOP_PREFERRED;
 
 #[cfg(target_has_atomic = "ptr")]
 use crate::sync::Arc;
@@ -723,7 +725,8 @@ impl fmt::Debug for CString {
 }
 
 #[stable(feature = "cstring_into", since = "1.7.0")]
-impl From<CString> for Vec<u8, Global, DEFAULT_COOP_PREFERRED> {
+#[allow(unused_braces)]
+impl From<CString> for Vec<u8, Global, {DEFAULT_COOP_PREFERRED!()}> {
     /// Converts a [`CString`] into a <code>[Vec]<[u8]></code>.
     ///
     /// The conversion consumes the [`CString`], and removes the terminating NUL byte.

library/alloc/src/lib.rs

@@ -185,6 +185,7 @@
 #![feature(global_co_alloc_short_term_pref)]
 #![feature(hashmap_internals)]
 #![feature(lang_items)]
+#![feature(global_co_alloc_def)]
 // When we used min_specialization instead of specialization, library/alloc/src/vec/mod.rs was failing with:
 // - cannot specialize on predicate `the constant `core::alloc::co_alloc_metadata_num_slots::<A>()` can be evaluated`
 // - cannot specialize on predicate `[(); _] well-formed`

library/alloc/src/raw_vec.rs

@@ -14,7 +14,7 @@ use crate::alloc::{Allocator, Global, Layout};
 use crate::boxed::Box;
 use crate::collections::TryReserveError;
 use crate::collections::TryReserveErrorKind::*;
-use crate::vec::DEFAULT_COOP_PREFERRED;
+use crate::DEFAULT_COOP_PREFERRED;
 
 #[cfg(test)]
 mod tests;
@@ -50,10 +50,11 @@ enum AllocInit {
 /// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
 /// `Box<[T]>`, since `capacity()` won't yield the length.
 #[allow(missing_debug_implementations)]
+#[allow(unused_braces)]
 pub(crate) struct RawVec<
     T,
     A: Allocator = Global,
-    const COOP_PREFERRED: bool = DEFAULT_COOP_PREFERRED,
+    const COOP_PREFERRED: bool = {DEFAULT_COOP_PREFERRED!()},
 > where
     [(); alloc::co_alloc_metadata_num_slots_with_preference_specific::<A>(COOP_PREFERRED)]:,
 {

library/alloc/src/string.rs

@@ -75,7 +75,7 @@ use crate::str::{self, from_utf8_unchecked_mut, Chars, Utf8Error};
 #[cfg(not(no_global_oom_handling))]
 use crate::str::{from_boxed_utf8_unchecked, FromStr};
 use crate::vec::Vec;
-use crate::vec::DEFAULT_COOP_PREFERRED;
+use crate::DEFAULT_COOP_PREFERRED;
 
 /// A UTF-8–encoded, growable string.
 ///
@@ -369,7 +369,8 @@ use crate::vec::DEFAULT_COOP_PREFERRED;
 #[derive(PartialOrd, Eq, Ord)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), lang = "String")]
-pub struct String<const COOP_PREFERRED: bool = DEFAULT_COOP_PREFERRED>
+#[allow(unused_braces)]
+pub struct String<const COOP_PREFERRED: bool = {DEFAULT_COOP_PREFERRED!()}>
 where
     [(); crate::co_alloc_metadata_num_slots_with_preference_global(COOP_PREFERRED)]:,
 {
@@ -2639,7 +2640,8 @@ where
 /// [`Display`]: fmt::Display
 #[cfg_attr(not(test), rustc_diagnostic_item = "ToString")]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait ToString<const COOP_PREFERRED: bool = DEFAULT_COOP_PREFERRED>
+#[allow(unused_braces)]
+pub trait ToString<const COOP_PREFERRED: bool = {DEFAULT_COOP_PREFERRED!()}>
 where
     [(); crate::co_alloc_metadata_num_slots_with_preference_global(COOP_PREFERRED)]:,
 {
@@ -3088,7 +3090,8 @@ where
 ///
 /// [`drain`]: String::drain
 #[stable(feature = "drain", since = "1.6.0")]
-pub struct Drain<'a, const COOP_PREFERRED: bool = DEFAULT_COOP_PREFERRED>
+#[allow(unused_braces)]
+pub struct Drain<'a, const COOP_PREFERRED: bool = {DEFAULT_COOP_PREFERRED!()}>
 where
     [(); crate::co_alloc_metadata_num_slots_with_preference_global(COOP_PREFERRED)]:,
 {

library/alloc/src/vec/drain.rs

@@ -19,11 +19,12 @@ use super::Vec;
 /// let iter: std::vec::Drain<_> = v.drain(..);
 /// ```
 #[stable(feature = "drain", since = "1.6.0")]
+#[allow(unused_braces)]
 pub struct Drain<
     'a,
     T: 'a,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global,
-    const COOP_PREFERRED: bool = { alloc::SHORT_TERM_VEC_PREFERS_COOP },
+    const COOP_PREFERRED: bool = { SHORT_TERM_VEC_PREFERS_COOP!() },
 > where
     [(); alloc::co_alloc_metadata_num_slots_with_preference_specific::<A>(COOP_PREFERRED)]:,
 {

library/alloc/src/vec/in_place_collect.rs

@@ -141,6 +141,9 @@ use core::iter::{InPlaceIterable, SourceIter, TrustedRandomAccessNoCoerce};
 use core::mem::{self, ManuallyDrop, SizedTypeProperties};
 use core::ptr::{self};
 
+use crate::Global;
+use crate::DEFAULT_COOP_PREFERRED;
+
 use super::{InPlaceDrop, InPlaceDstBufDrop, SpecFromIter, SpecFromIterNested, Vec};
 
 /// Specialization marker for collecting an iterator pipeline into a Vec while reusing the
@@ -150,7 +153,8 @@ pub(super) trait InPlaceIterableMarker {}
 
 impl<T> InPlaceIterableMarker for T where T: InPlaceIterable {}
 
-impl<T, I> SpecFromIter<T, I> for Vec<T, Global, DEFAULT_COOP_PREFERRED>
+#[allow(unused_braces)]
+impl<T, I> SpecFromIter<T, I> for Vec<T, Global, {DEFAULT_COOP_PREFERRED!()}>
 where
     I: Iterator<Item = T> + SourceIter<Source: AsVecIntoIter> + InPlaceIterableMarker,
 {